When you add a customer or business customer, you can assign a payment method to the company.Future invoices for sales orders made by this customer will be defaulted to this payment method. If you do not assign a payment method to the customer the default payment method set up in you general settings will be used.
To assign a payment method to a customer first go to the Relationships section and select the customer you want to assign a payment method to.
Click to Edit the customer information.
You will see a dropdown box called Default Payment Method. Click to view and select your payment method options.
Save your option.
When you create a Sales order for this customer from this point, this default payment method will be applied to the order.